Functionalized polymer, rubber composition and pneumatic tire

ABSTRACT

The present invention is directed to a functionalized elastomer comprising the reaction product of a living anionic elastomeric polymer and a polymerization terminator of formula I 
     
       
         
         
             
             
         
       
     
     wherein R 1 , R 2 , R 3 , R 4 , and R 5  are as defined. The invention is further directed to a rubber composition including the functionalized elastomer, and a pneumatic tire including the rubber composition.

BACKGROUND OF THE INVENTION

In recent years, there is a growing demand for functionalized polymers.Functionalized polymers can be synthesized through variousliving/controlled polymerization techniques. In the livingpolymerization process based on active carbanionic center, metals fromGroups I and II of the periodic table are commonly used to initiate thepolymerization of monomers into polymers. For example, lithium, barium,magnesium, sodium, and potassium are metals that are frequently utilizedin such polymerizations. Initiator systems of this type are ofcommercial importance because they can be used to produce stereoregulated polymers. For instance, lithium initiators can be utilized toinitiate the anionic polymerization of isoprene into syntheticpolyisoprene rubber or to initiate the polymerization of 1,3-butadieneinto polybutadiene rubber having the desired microstructure.

The polymers formed in such polymerizations have the metal used toinitiate the polymerization at the growing end of their polymer chainsand are sometimes referred to as living polymers. They are referred toas living polymers because their polymer chains which contain theterminal metal initiator continue to grow or live until all of theavailable monomer is exhausted. Polymers that are prepared by utilizingsuch metal initiators normally have structures which are essentiallylinear and normally do not contain appreciable amounts of branching.

This invention details synthesis of functionalized polymers and theiruse in rubber formulation and tire materials. In general to achieve thebest tire performance properties functionalized polymers are highlydesirable. In order to reduce the rolling resistance and to improve thetread wear characteristics of tires, functionalized elastomers having ahigh rebound physical property (low hysteresis) have been used for thetire tread rubber compositions. However, in order to increase the wetskid resistance of a tire tread, rubbery polymers that have a relativelylower rebound physical property (higher hysteresis) which therebyundergo a greater energy loss, have sometimes been used for such treadrubber compositions. To achieve such relatively inconsistentviscoelastic properties for the tire tread rubber compositions, blends(mixtures) of various types of synthetic and natural rubber can beutilized in tire treads.

Functionalized rubbery polymers made by living polymerization techniquesare typically compounded with sulfur, accelerators, antidegradants, afiller, such as carbon black, silica or starch, and other desired rubberchemicals and are then subsequently vulcanized or cured into the form ofa useful article, such as a tire or a power transmission belt. It hasbeen established that the physical properties of such cured rubbersdepend upon the degree to which the filler is homogeneously dispersedthroughout the rubber. This is in turn related to the level of affinitythat filler has for the particular rubbery polymer. This can be ofpractical importance in improving the physical characteristics of rubberarticles which are made utilizing such rubber compositions. For example,the rolling resistance and traction characteristics of tires can beimproved by improving the affinity of carbon black and/or silica to therubbery polymer utilized therein. Therefore, it would be highlydesirable to improve the affinity of a given rubbery polymer forfillers, such as carbon black and silica.

In tire tread formulations, better interaction between the filler andthe rubbery polymer results in lower hysteresis and consequently tiresmade with such rubber formulations have lower rolling resistance. Lowtan delta values at 60° C. are indicative of low hysteresis andconsequently tires made utilizing such rubber formulations with low tandelta values at 60° C. normally exhibit lower rolling resistance. Betterinteraction between the filler and the rubbery polymer in tire treadformulations also typically results higher tan delta values at 0° C.which is indicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to acombination of physical absorption (van der Waals force) andchemisorption between the oxygen containing functional groups on thecarbon black surface and the rubber (see D. Rivin, J. Aron, and A.Medalia, Rubber Chem. & Technol. 41, 330 (1968) and A. Gessler, W. Hess,and A Medalia, Plast. Rubber Process, 3, 141 (1968)). Various otherchemical modification techniques, especially for styrene-butadienerubber made by solution polymerization (S-SBR), have also been describedfor reducing hysteresis loss by improving polymer-filler interactions.In one of these techniques, the solution rubber chain end is modifiedwith aminobenzophenone. This greatly improves the interaction betweenthe polymer and the oxygen-containing groups on the carbon black surface(see N. Nagata, Nippon Gomu Kyokaishi, 62, 630 (1989)). Tin coupling ofanionic solution polymers is another commonly used chain endmodification method that aids polymer-filler interaction supposedlythrough increased reaction with the quinone groups on the carbon blacksurface. The effect of this interaction is to reduce the aggregationbetween carbon black particles which in turn, improves dispersion andultimately reduces hysteresis.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. Such functionalizedpolymers can be beneficially used in manufacturing tires and otherrubber products where improved polymer/filler interaction is desirable.In tire tread compounds this can result in lower polymer hysteresiswhich in turn can provide a lower level of tire rolling resistance.

The present invention is directed to a functionalized elastomercomprising the reaction product of a living anionic elastomeric polymerand a polymerization terminator of formula I

wherein:

R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy withthe proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy;

R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, orC1 to C8 arylalkanediyl; Si is silicon; S is sulfur;

X is —O—R⁶ or

wherein O is oxygen; N is nitrogen; and

i) R⁵ is —(CH₂)₂—C(═O)— wherein the (CH₂)₂ group is adjacent to thesulfur and R⁶ and R⁷ are independently hydrogen or C1 to C8 alkyl, C1 toC8 aryl, C1 to C8 alkylaryl, or C1 to C8 arylalkyl; or

ii) R⁵ and R⁶ taken together with the heteroatom nitrogen or heteroatomoxygen to which both R⁵ and R⁶ are attached form a 5 membered ringwherein R⁵ is —CH—C(═O)— wherein the carbonyl group is adjacent to theheteroatom and R⁶ is —CH₂—C(═O)— wherein the carbonyl group is adjacentto the heteroatom and R⁷ is hydrogen or C1 to C8 alkyl, C1 to C8 aryl,C1 to C8 alkylaryl, or C1 to C8 arylalkyl.

The invention is further directed to a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the ¹H NMR of propanamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thiol]-.

FIG. 2 shows the ¹H NMR of 2,5-pyrrolidinedione,1-methyl-3-[[3-(triethoxysilyl)propyl]thiol]-.

FIG. 3 shows graphs of G′, G″ and tan delta versus strain fornon-productive samples with silane coupling agent.

FIG. 4 shows graphs of G′, G″ and tan delta versus strain fornon-productive samples without silane coupling agent.

FIG. 5 shows a cure curve obtained at 7% strain for productive batcheswith silane coupling agent.

FIG. 6 shows graphs of G′, G″ and tan delta versus strain for productivesamples with silane coupling agent.

FIG. 7 shows a cure curve obtained at 7% strain for productive batcheswithout silane coupling agent.

FIG. 8 shows graphs of G′, G″ and tan delta versus strain for productivesamples without silane coupling agent.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a functionalized elastomer comprising the reactionproduct of a living anionic elastomeric polymer and a polymerizationterminator of formula I

wherein:

R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy withthe proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy;

R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, orC1 to C8 arylalkanediyl; Si is silicon; S is sulfur;

X is —O—R⁶ or

wherein O is oxygen; N is nitrogen; and

i) R⁵ is —(CH₂)₂—C(═O)— wherein the (CH₂)₂ group is adjacent to thesulfur and R⁶ and R⁷ are independently hydrogen or C1 to C8 alkyl, C1 toC8 aryl, C1 to C8 alkylaryl, or C1 to C8 arylalkyl; or

ii) R⁵ and R⁶ taken together with the heteroatom nitrogen or heteroatomoxygen to which both R⁵ and R⁶ are attached form a 5 membered ringwherein R⁵ is —CH—C(═O)—wherein the carbonyl group is adjacent to theheteroatom and R⁶ is —CH₂—C(═O)— wherein the carbonyl group is adjacentto the heteroatom and R⁷ is hydrogen or C1 to C8 alkyl, C1 to C8 aryl,C1 to C8 alkylaryl, or C1 to C8 arylalkyl.

There is further disclosed a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition.

The subject invention provides a means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. The process of thepresent invention can be used to functionalize any living polymer whichis terminated with a metal of group I or II of the periodic table. Thesepolymers can be produced utilizing techniques that are well known topersons skilled in the art. The metal terminated rubbery polymers thatcan be functionalized with a terminator of formula I in accordance withthis invention can be made utilizing monofunctional initiators havingthe general structural formula P-M, wherein P represents a polymer chainand wherein M represents a metal of group I or II. The metal initiatorsutilized in the synthesis of such metal terminated polymers can also bemultifunctional organometallic compounds. For instance, difunctionalorganometallic compounds can be utilized to initiate suchpolymerizations. The utilization of such difunctional organometalliccompounds as initiators generally results in the formation of polymershaving the general structural formula M-P-M, wherein P represents apolymer chain and wherein M represents a metal of group I or II. Suchpolymers which are terminated at both of their chain ends with a metalfrom group I or II also can be reacted with terminator of formula I tofunctionalize both of their chain ends. It is believed that utilizingdifunctional initiators so that both ends of the polymers chain can befunctionalized with the terminator of formula I can further improveinteraction with fillers, such as carbon black and silica.

The initiator used to initiate the polymerization employed insynthesizing the living rubbery polymer that is functionalized inaccordance with this invention is typically selected from the groupconsisting of barium, lithium, magnesium, sodium, and potassium. Lithiumand magnesium are the metals that are most commonly utilized in thesynthesis of such metal terminated polymers (living polymers). Normally,lithium initiators are more preferred.

Organolithium compounds are the preferred initiators for utilization insuch polymerizations. The organolithium compounds which are utilized asinitiators are normally organo monolithium compounds. The organolithiumcompounds which are preferred as initiators are monofunctional compoundswhich can be represented by the formula: R—Li, wherein R represents ahydrocarbyl radical containing from 1 to about 20 carbon atoms.Generally, such monofunctional organolithium compounds will contain from1 to about 10 carbon atoms. Some representative examples of preferredbutyllithium, secbutyllithium, n-hexyllithium, n-octyllithium,tertoctyllithium, n-decyllithium, phenyllithium, 1-naphthyllithium,4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium,cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Secondary-butyllithium is a highly preferredorganolithium initiator. Very finely divided lithium having an averageparticle diameter of less than 2 microns can also be employed as theinitiator for the synthesis of living rubbery polymers that can befunctionalized with a terminator of formula I in accordance with thisinvention. U.S. Pat. No. 4,048,420, which is incorporated herein byreference in its entirety, describes the synthesis of lithium terminatedliving polymers utilizing finely divided lithium as the initiator.Lithium amides can also be used as the initiator in the synthesis ofliving polydiene rubbers (see U.S. Pat. No. 4,935,471 the teaching ofwhich are incorporated herein by reference with respect to lithiumamides that can be used as initiators in the synthesis of living rubberypolymer).

The amount of organolithium initiator utilized will vary depending uponthe molecular weight which is desired for the rubbery polymer beingsynthesized as well as the precise polymerization temperature which willbe employed. The precise amount of organolithium compound required toproduce a polymer of a desired molecular weight can be easilyascertained by persons skilled in the art. However, as a general rulefrom 0.01 to 1 phm (parts per 100 parts by weight of monomer) of anorganolithium initiator will be utilized. In most cases, from 0.01 to0.1 phm of an organolithium initiator will be utilized with it beingpreferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon doublebonds can be polymerized into polymers using such metal catalysts.Elastomeric or rubbery polymers can be synthesized by polymerizing dienemonomers utilizing this type of metal initiator system. The dienemonomers that can be polymerized into synthetic rubbery polymers can beeither conjugated or nonconjugated diolefins. Conjugated diolefinmonomers containing from 4 to 8 carbon atoms are generally preferred.Vinyl-substituted aromatic monomers can also be copolymerized with oneor more diene monomers into rubbery polymers, for examplestyrene-butadiene rubber (SBR). Some representative examples ofconjugated diene monomers that can be polymerized into rubbery polymersinclude 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene,2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and4,5-diethyl-1,3-octadiene. Some representative examples ofvinyl-substituted aromatic monomers that can be utilized in thesynthesis of rubbery polymers include styrene, 1-vinylnapthalene,3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene,3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene,6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene,α-methylstyrene, and the like.

The metal terminated rubbery polymers that are functionalized with aterminator of formula I in accordance with this invention are generallyprepared by solution polymerizations that utilize inert organicsolvents, such as saturated aliphatic hydrocarbons, aromatichydrocarbons, or ethers. The solvents used in such solutionpolymerizations will normally contain from about 4 to about 10 carbonatoms per molecule and will be liquids under the conditions of thepolymerization. Some representative examples of suitable organicsolvents include pentane, isooctane, cyclohexane, normal-hexane,benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, and the like,alone or in admixture. For instance, the solvent can be a mixture ofdifferent hexane isomers. Such solution polymerizations result in theformation of a polymer cement (a highly viscous solution of thepolymer).

The metal terminated living rubbery polymers utilized in the practice ofthis invention can be of virtually any molecular weight. However, thenumber average molecular weight of the living rubbery polymer willtypically be within the range of about 50,000 to about 500,000. It ismore typical for such living rubbery polymers to have number averagemolecular weights within the range of 100,000 to 250,000.

The metal terminated living rubbery polymer can be functionalized bysimply adding a stoichiometric amount of a terminator of formula I to asolution of the rubbery polymer (a rubber cement of the living polymer).In other words, approximately one mole of the terminator of formula I isadded per mole of terminal metal groups in the living rubbery polymer.The number of moles of metal end groups in such polymers is assumed tobe the number of moles of the metal utilized in the initiator. It is, ofcourse, possible to add greater than a stoichiometric amount of theterminator of formula I. However, the utilization of greater amounts isnot beneficial to final polymer properties. Nevertheless, in many casesit will be desirable to utilize a slight excess of the terminator offormula I to insure that at least a stoichiometric amount is actuallyemployed or to control the stoichiometry of the functionalizationreaction. In most cases from about 0.8 to about 1.1 moles of theterminator of formula I will be utilized per mole of metal end groups inthe living polymer being treated. In the event that it is not desired tofunctionalize all of the metal terminated chain ends in a rubberypolymer then, of course, lesser amounts of the terminator of formula Ican be utilized.

The terminator of formula I will react with the metal terminated livingrubbery polymer over a very wide temperature range. For practicalreasons the functionalization of such living rubbery polymers willnormally be carried out at a temperature within the range of 0° C. to150° C. In order to increase reaction rates, in most cases it will bepreferred to utilize a temperature within the range of 20° C. to 100° C.with temperatures within the range of 50° C. to 80° C. being mostpreferred. The capping reaction is very rapid and only very shortreaction times within the range of 0.5 to 4 hours are normally required.However, in some cases reaction times of up to about 24 hours may beemployed to insure maximum conversions.

After the functionalization reaction is completed, it will normally bedesirable to “kill” any living polydiene chains which remain. This canbe accomplished by adding an alcohol, such as methanol or ethanol, tothe polymer cement after the functionalization reaction is completed inorder to eliminate any living polymer that was not consumed by thereaction with the terminator of formula I. The end-group functionalizedpolydiene rubber can then be recovered from the solution utilizingstandard techniques.

The functionalized polymer may be compounded into a rubber composition.

The rubber composition may optionally include, in addition to thefunctionalized polymer, one or more rubbers or elastomers containingolefinic unsaturation. The phrases “rubber or elastomer containingolefinic unsaturation” or “diene based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polyisoprene (natural or synthetic), polybutadiene andSBR.

In one aspect the at least one additional rubber is preferably of atleast two of diene based rubbers. For example, a combination of two ormore rubbers is preferred such as cis 1,4-polyisoprene rubber (naturalor synthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, c is 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, c is 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil.Processing oil may be included in the rubber composition as extendingoil typically used to extend elastomers. Processing oil may also beincluded in the rubber composition by addition of the oil directlyduring rubber compounding. The processing oil used may include bothextending oil present in the elastomers, and process oil added duringcompounding. Suitable process oils include various oils as are known inthe art, including aromatic, paraffinic, naphthenic, vegetable oils, andlow PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.Suitable low PCA oils include those having a polycyclic aromatic contentof less than 3 percent by weight as determined by the IP346 method.Procedures for the IP346 method may be found in Standard Methods forAnalysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr ofsilica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), crosslinked particulate polymer gels includingbut not limited to those disclosed in U.S. Pat. Nos. 6,242,534;6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment the rubber composition may contain a conventionalsulfur containing organosilicon compound. In one embodiment, the sulfurcontaining organosilicon compounds are the 3,3′-bis(trimethoxy ortriethoxy silylpropyl) polysulfides. In one embodiment, the sulfurcontaining organosilicon compounds are 3,3′-bis(triethoxysilylpropyl)disulfide and/or 3,3′-bis(triethoxysilylpropyl)tetrasulfide.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

Example 1 Synthesis of propaneamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thio]-

Synthesis of siloxy functionalized acrylamide is based on thiol-enereaction mechanism in which thiol is 3-mercaptopropyltriethoxysilane andene is N,N-dimethylacrylamide. Triethylamine was used as catalyst whichinitiates the formation of enolate in synthesis of the siloxyfunctionalized acrylamide.

To a stirred solution of 3-(mercaptopropyl)triethoxysilane (30 mmol) in50 mL of anhydrous ethanol was added N,N-dimethylacrylamide (30 mmol) atambient temperature. To the solution of reactants was addedtriethylamine (30 mmol) and resulting solution was stirred at ambienttemperature for 48 h. The mixture was concentrated under reducedpressure and dried overnight in Schlenk line. The product was obtainedin 90% yield. The synthesized compound was characterized via ¹H-NMR (400MHz) and HPLC (88.4% purity). The chemical structures were characterizedvia NMR (400 MHz) as shown in FIG. 1.

Example 2 Synthesis of 2,5-pyrrolidinedione,1-methyl-3-[[3-(triethoxysilyl)propyl]thio]-

Synthesis of siloxy functionalized maleimide is based on thiol-enereaction mechanism in which thiol is 3-mercaptopropyltriethoxysilane andene is N-methylmaleimide. Triethylamine was used as catalyst whichinitiates the formation of enolate in synthesis of siloxy functionalizedmaleimide.

To 250 mL round bottomed flask, maleimide (30 mmol) and 50 mL ethanolwas added. To this solution 3-(mercaptopropyltriethoxysilane) (30 mmol)and triethylamine (15 mmol) was added and mixture was stirred for 2.5 hat ambient temperature. The mixture was concentrated under reducedpressure and dried overnight in Schlenk line. The product was obtainedin 91% yield. The synthesized compound was characterized via ¹H-NMR (400MHz) and HPLC (95.8% purity)/The chemical structures were characterizedvia NMR (400 MHz) as shown in FIG. 2.

Example 3 Co-Polymerization of Styrene and Butadiene

Polymerizations were done in a 1 gallon reactor at 65° C. Monomer premixof styrene and butadiene was charged into reactor with hexane as solventfollowed by addition of modifier (TMEDA) and initiator (n-butyllithium).When the conversion was above 98%, the polymerizations were terminatedwith isopropanol or with functional terminator propanamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thio]- from Example 1, or2,5-pyrrolidinedione, 1-methyl-3-[[3-(triethoxysilyl)propyl]thio]- fromExample 2.

The polymers obtained were characterized using different techniques, forexample, size exclusion chromotography (SEC) for determination ofmolecular weight, dynamic scanning calorimetry (DSC) for determinationof Tg, IR for determining cis, trans, styrene and vinyl content, andMooney viscosity measurements with results given in Tables 1 and 2.

TABLE 1 Overall Mn Polymer Sample (g/mol) PDI 1: Sulfanylsilane-SBR¹250,000 1.42 (Comparative) 2: SBR² (Control) 182,000 1.02 3:Acrylamide-SBR³ 248,000 1.41 4: Maleimide-SBR⁴ 218,000 1.17¹Sulfanylsilane functionalized solution polymerized styrene-butadienerubber, available commercially as Sprintan ® SLR 4602, from Styron.²Solution polymerized styrene-butadiene rubber terminated usingisopropanol, from The Goodyear Tire & Rubber Company. ³Solutionpolymerized styrene-butadiene terminated with propanamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thio]-. ⁴Solution polymerizedstyrene-butadiene terminated with 2,5-pyrrolidinedione,1-methyl-3-[[3-(triethoxysilyl)propyl]thio]-.

TABLE 2 Polymer Sample Mooney Cis Trans Styrene Vinyl¹ Tg (° C.) 1:Sulfanylsilane- 65 12.15 21.88 17.97 48 −25.0 SBR (Comparative) 2: Non-35.9 13.07 18.29 23.70 44.94 −22.1 functionalized- SBR (Control) 3:Acrylamide- 46.3 11.88 21.99 26.90 39.33 −22.2 SBR 4: Maleimide- 57.913.02 18.39 25.06 43.52 −22.0 SBR ¹Vinyl content expressed as weightpercent based on total polymer weight.

Example 4 Mixing Studies and Compound Testing

Each of the functionalized SBR copolymers of Example 3 (functionalizedusing siloxy acrylamide {propanamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thio]-} and siloxy maleimide{2,5-pyrrolidinedione, 1-methyl-3-[[3-(triethoxysilyl)propyl]thio]-} aswell as control and a comparative sulfanylsilane functionalized SBR wereused to make rubber compounds.

Rubber compounds were mixed in a 3-piece 75 mL CW Brabender® mixerequipped with Banbury® rotor. Each SBR sample was mixed with additivesin a three stage mix procedure as shown in Table 3, with all amountsgiven in parts by weight, per 100 parts by weight of elastomer (phr). Inthe first non-productive mix stage, compounds were mixed for 4 minutesat 60 rpm using 140° C. as starting temperature. All compounds werepressed in a compression molding machine for 1 minute before a secondnon-productive mix stage. In the second non productive step mixingconditions were the same as in the first non-productive step, with mixtime of 3 minutes. Productive mixes were carried out using 60° C.starting temperature and 60 rpm with mix time of 3 minute.

TABLE 3 Variable (Addition as indicated in Examples 5-8) Silane¹ 5.2First Non Productive Step SBR 100 Silica 65 Process Oil 30 Stearic Acid2 Zinc Oxide 3.5 Second Non Productive Step Remixing Productive Mix StepSulfur 1.7 Accelerators² 3.1 Antidegradant 0.75¹Bis(triethoxysilylpropyl) disulfide ²Sulfenamide and guanidine types

The compounds were tested for silica interaction using an RPA 2000® fromAlpha Technology. Non-productive compounds were first heated to 160° C.and the torque increase was monitored as a function of time using 1 Hzand 0.48% strain in order to determine the rate of the filler“flocculation”. Subsequently the compounds were cooled to 40° C. and astrain sweep was carried out using 1 Hz in order to determine the Payneeffect, i.e., the strain dependence of G′, G″ and tan delta. Cure wascarried out at 160° C. using 7% strain. Cured compounds dynamicproperties were measured first by curing the sample at 160° C. for 30minute at the lowest possible strain to mimic a static cure. After thissamples were cooled and tested in the given manner for green compounds.

Example 5 Samples 5-8: Nonproductive Compound with Added Silane CouplingAgent

FIG. 3 shows the results of the strain sweeps conducted at 40° C. on thenon-productive compounds with silane coupling agent after 30 minutesheat treatment of the samples at low strain at 160° C. in the RPA. Asshown in FIG. 3, G′ and tan delta of non-functionalized control sample 6shows highest strain dependency. The comparative sulfanylsilanefunctionalized polymer (sample 5), siloxy acrylamide (sample 7) andsiloxy maleimide (sample 8) functionalized polymer shows reduced straindependency which indicates less filler-filler interaction or more fillerpolymer interaction.

The ratio of the low amplitude (0.48% strain) modulus (LAM) and highamplitude (100% strain) modulus (HAM) is a measure of the Payne effectand is given in Table 4 for the various samples. Higher the LAM/HAMratio less is polymer-filler interaction. As shown in Table 4,non-functionalized control polymer sample shows highest LAM/HAM valueindicating least polymer-filler interaction while sulfanylsilane, siloxyacrylamide and siloxy maleimide functionalized polymer shows lowerLAM/HAM ratio.

TABLE 4 SBR Sample LAM/HAM Tan Delta (40° C.) (5% strain) 5(Sulfanylsilane-SBR) 7.2 0.19 6 (Control) 18.9 0.26 7 (Acrylamide-SBR)10.3 0.25 8 (Maleimide-SBR) 10.5 0.24

Example 6 Samples 9-12: Non-Productive Compound with Added SilaneCoupling Agent

FIG. 4 shows the results of the strain sweeps conducted at 40° C. on thenon-productive compounds without any silane coupling agent after 30minutes heat treatment of the samples at low strain at 160° C. in theRPA. In this case no coupling agent was added to evaluate solelyinteraction between polymer chain ends and filler. In this case, similarto results obtained when coupling agent was used, G′ and tan delta ofcontrol polymer sample shows highest strain dependency. Sulfanylsilane(sample 9), siloxy acrylamide (sample 11) and siloxy maleimide (sample12) functionalized polymer samples shows reduced strain dependency.

The ratio of the low amplitude (0.48% strain) and high amplitude (100%strain) moduli is shown in Table 5. Without the use of silane couplingagent, Payne effect is enhanced as compared to Payne effect observedwith the use of silane coupling agent. The control sample shows highestLAM/HAM value, i.e., relatively high Payne effect. Sulfanylsilane,siloxy acrylamide and siloxy maleimide functionalized polymer showslower Payne effect indicating good polymer-filler interaction. As theresult of good polymer-filler interaction, tan delta values for thesulfanylsilane, siloxy acrylamide and siloxy maleimide functionalizedpolymers are lower than non-functionalized control.

TABLE 5 SBR Sample No. LAM/HAM Tan Delta (40° C.) (5% strain)  9(Sulfanylsilane-SBR) 17.5 0.22 10 (Control) 53.8 0.43 11(Acrylamide-SBR) 25.9 0.32 12 (Maleimide-SBR) 28.0 0.33

Example 7 Samples 13-16: Productive Compound with Added Silane CouplingAgent

In this example, the addition of silane in productive compound isillustrated. Compound mixing was done with a first non-productive mixstage followed by the second non-productive step and finally productivestep. Addition of the silane coupling agent was done in the firstnon-productive mix stage.

The cure curves obtained with silane coupling agent at 7% strain isshown in FIG. 5. Cure parameters max torque S′ max and change in torquedelta S′ are given in Table 6.

TABLE 6 Maximum and delta torque values for productive batches withsilane coupling agent SBR Sample No. S′max (dN * m) Delta S′ (dN * m) 13(Sulfanylsilane-SBR) 11.18 9.08 14 (Control) 15.7 14.56 15(Acrylamide-SBR) 14.27 13.05 16 (Maleimide-SBR) 15.87 14.49

The strain sweeps were conducted in separate RPA runs. In these runs thesamples were cured at 160° C. for 30 minutes using the lowest possiblestrain (0.28%) in order to mimic static cure and not to alterfiller-filler or filler-polymer interaction. Strain sweep cures wereobtained at 40° C. as shown in FIG. 6.

The ratio of the low amplitude (0.48% strain) and high amplitude (100%strain) moduli is shown in Table 7. The strain sweeps conducted on thecured compounds indicates that siloxy acrylamide and siloxy maleimidefunctionalized polymer samples shows lower Payne effect than thesulfanylsilane functionalized polymer, so improved polymer fillerinteraction.

TABLE 7 Tan Delta Tan Delta (30° C.) (40° C.) (5% (10% strain) SBRSample No. LAM/HAM strain) ARES strain sweep 1 Sulfanylsilane-SBR 3.20.14 0.16 2 Control 4.8 0.18 0.18 3 Acrylamide-SBR 2.4 0.15 0.16 4Maleimide-SBR 2.3 0.14 0.16

Example 8 Productive Compounds without Added Silane Coupling Agent

In this example, mixing of productive compound without addition ofsilane coupling agent is illustrated. Compound mixing was done similarto one used for productive batches with silane coupling agent. The curecurve for productive sample without silane coupling agent at 7% strainis shown in FIG. 7. Cure parameters max torque S′ max and change intorque delta S′ are given in Table 8.

TABLE 8 SBR Sample No. S′max (dN * m) Delta S′ (dN * m) 1Sulfanylsilane-SBR 25.42 15.99 2 Control 24.72 18.21 3 Acrylamide-SBR27.14 16.04 4 Maleimide-SBR 26.79 18.24

The strain sweeps were conducted in separate RPA runs. In these runs thesample were cured at 160° C. for 30 minutes using the lowest possiblestrain (0.28%) in order to mimic static cure and not to alterfiller-filler or filler-polymer interaction. The ratio of the lowamplitude (0.48% strain) and high amplitude (100% strain) moduli isshown in Table 9. Strain sweep curves were obtained at 40° C. as shownin FIG. 8.

TABLE 9 Tan Delta (30° C.) Tan Delta (10% strain) SBR Sample No. LAM/HAM(5% strain) ARES strain sweep 1 Sulfanylsilane-SBR 8.7 0.13 0.18 2Control 16.2 0.21 0.18 3 Acrylamide-SBR 12.1 0.15 0.19 4 Maleimide-SBR12.6 0.17 0.18

The strain sweeps conducted on the cured compounds indicates that siloxyacrylamide and siloxy maleimide functionalized polymer shows reducedPayne effect, indicating improved polymer filler interaction compared tonon-functionalized polymer control. In addition, tan delta values forsulfanylsilane and siloxy acrylamide and siloxy maleimide functionalizedpolymers are lower as compared to non-functionalized control sample.

As shown above, both comparative and siloxy acrylamide and siloxymaleimide functionalized polymer samples shows reduced Payne effect aswell lower tan delta values as compared to non-functionalized controlsample. This can be explained by difference in end groups which arepresent in these polymers.

In the comparative polymer, it is assumed that the polymer is terminatedusing end terminating agent based on siloxy and sulfur silane groups asdescribed in patent publication US2008/0287601. Without wishing to bebound by any theory, for the polymer chain carrying both siloxy as wellsulfur-silane groups, the siloxy groups help in providing covalentinteraction with silica surface and sulfur protected with silane helpsin providing interaction between polymer chains. The sulfur-silane grouphas the potential to cleave off during mixing and therefore results ingeneration of active thiol groups which can help in achievingcross-linking between polymer chains. In addition, the comparativepolymer is likely coupled with an agent such as SnCl₄ which can help inachieving better processabilty.

The siloxy acrylamide and siloxy maleimide functionalized polymersamples of the present invention are terminated using end terminatingagent based on siloxy and dimethyl acrylamide or methyl maleimidegroups. Again, while not wishing to be bound by any theory, it isthought that similar to the comparative polymer, siloxy groups helps inproviding covalent interaction with silica and amine groups helps inachieving good interaction between polymer chains and silica. Whensiloxy functionalized acrylamide or maleimide is used as end terminatingagent, there is the possibility of active polymer chain to be attachedto terminating agent group via nucleophilic displacement of alkoxy groupas well as polymer chain can also be attached at carbonyl bond. Polymerchain attached to siloxy group helps in attaining good interactionbetween polymer chain and filler. In contrast to the comparativesulfanysilane functionalized polymer, with the use of siloxy acrylamideor siloxy maleimide end terminating agent, it is also possible toachieve coupling between polymer chains without addition of anyadditional SnCl₄ because the end terminating agent based on siloxyacrylamide or maleimide group might interact with living anionic polymerchain in two different ways. One way is substitution of ethoxide grouppresent on siloxy acrylamide or maleimide with polymer chain and secondway is reaction of anionic polymer chain with carbonyl group. Thistheorized mechanism of action of siloxy acrylamide and siloxy maleimideend terminating agent is shown in Scheme 1 and 2. Here, P⁺Li⁻ indicatesthe living polymer P with the lithium end group Li.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

What is claimed is:
 1. A functionalized elastomer comprising thereaction product of a living anionic elastomeric polymer and apolymerization terminator of formula I

wherein: R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8alkoxy with the proviso that at least two of R¹, R² and R³ are C1 to C8alkoxy; R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8alkylarylene, or C1 to C8 arylalkanediyl; Si is silicon; S is sulfur; Xis —O—R⁶ or

wherein O is oxygen; N is nitrogen; and i) R⁵ is —(CH₂)₂—C(═O)— whereinthe (CH₂)₂ group is adjacent to the sulfur and R⁶ and R⁷ areindependently hydrogen or C1 to C8 alkyl, C1 to C8 aryl, C1 to C8alkylaryl, or C1 to C8 arylalkyl; or ii) R⁵ and R⁶ taken together withthe heteroatom nitrogen or heteroatom oxygen to which both R⁵ and R⁶ areattached form a 5 membered ring wherein R⁵ is —CH—C(═O)— wherein thecarbonyl group is adjacent to the heteroatom and R⁶ is —CH₂—C(═O)—wherein the carbonyl group is adjacent to the heteroatom and R⁷ ishydrogen or C1 to C8 alkyl, C1 to C8 aryl, C1 to C8 alkylaryl, or C1 toC8 arylalkyl.
 2. The functionalized elastomer of claim 1, wherein R¹, R²and R³ are each C1 to C8 alkoxy.
 3. The functionalized elastomer ofclaim 1, wherein the living anionic elastomer is derived from at leastone diene monomer and optionally at least one vinyl aromatic monomer. 4.The functionalized elastomer of claim 1, wherein the living anionicelastomer is derived from at least one of isoprene and butadiene, andoptionally from styrene.
 5. The functionalized elastomer of claim 1,wherein the living anionic elastomer is derived from butadiene andstyrene.
 6. The functionalized elastomer of claim 1, wherein thepolymerization terminator of formula I is propaneamide,N,N-dimethyl-3-[[3-(triethoxysilyl)propyl]thio]-.
 7. The functionalizedelastomer of claim 1, wherein the polymerization terminator of formula Iis 2,5-pyrrolidinedione, 1-methyl-3-[[3-(triethoxysilyl)propyl]thio]-.8. The functionalized elastomer of claim 1, wherein the polymerizationterminator of formula I has the structure


9. The functionalized elastomer of claim 1, wherein the polymerizationterminator of formula I has the structure


10. A rubber composition comprising the functionalized elastomer ofclaim
 1. 11. The rubber composition of claim 10, further comprisingsilica.
 12. A pneumatic tire comprising the rubber composition of claim11.